1. Field of the Invention
This invention relates to personal alarm systems and in particular to such systems transmitting at a higher power level during emergencies.
2. Background Art
Personal alarm systems are well known in the art (see for example U.S. Pat. Nos. 4,777,478, 5,025,247, 5,115,223, 4,952,928, 4,819,860, 4,899,135, 5,047,750, 4,785,291, 5,043,702, and 5,086,391). These systems are used to maintain surveillance of children. They are used to monitor the safety of employees involved in dangerous work at remote locations. They are even used to find lost or stolen vehicles and strayed pets.
These systems use radio technology to link a remote transmitting unit with a base receiving and monitoring station. The remote unit is usually equipped with one or more hazard sensors and is worn or attached to the person or thing to be monitored. When a hazard is detected, the remote unit transmits to the receiving base station where an operator can take appropriate action in responding to the hazard.
The use of personal alarm systems to monitor the activities of children has become increasingly popular. A caretaker attaches a small remote unit, no larger than a personal pager, to an outer garment of a small child. If the child wanders off or is confronted with a detectable hazard, the caretaker is immediately notified and can come to the child's aid. In at least one interesting application, a remote unit includes a receiver and an audible alarm which can be activated by a small hand-held transmitter. The alarm is attached to a small child. If the child wanders away in a large crowd, such as in a department store, the caretaker actives the audible alarm which then emits a sequence of "beeps" useful in locating the child in the same way one finds a car at a parking lot through the use of an auto alarm system.
A number of novel features have been included in personal alarm systems. Hirsh et al., U.S. Pat. No. 4,777,478, provide for a panic button to be activated by the child, or an alarm to be given if someone attempts to remove the remote unit from the child's clothing. Banks, U.S. Pat. No. 5,025,247, teaches a base station which latches an alarm condition so that failure of the remote unit, once having given the alarm, will not cause the alarm to turn off before help is summoned. Moody, U.S. Pat. No. 5,115,223, teaches use of orbiting satellites and triangulation to limit the area of a search for a remote unit which has initiated an alarm. In U.S. Pat. No. 4,952,928 to Carroll et al., and in U.S. Pat. No. 4,819,860 to Hargrove et al., the apparatus provides for the remote monitoring of the vital signs of persons who are not confined to fixed locations.
Ghahariiran, U.S. Pat. No. 4,899,135, teaches a child monitoring device using radio or ultra-sonic frequency to give alarm if a child wanders out of range or falls into water. Hawthorne, U.S. Pat. 4,785,291, teaches a distance monitor for child surveillance in which a unit worn by the child includes a radio transmitter. As the child moves out of range, the received field strength, of a signal transmitted by the child's unit, falls below a limit and an alarm is given.
Clinical experience in the emergency rooms of our hospitals has taught that a limited number of common hazards account for a majority of the preventable injuries and deaths among our toddler age children. These hazards include the child's wandering away from a safe or supervised area, water emersion, fire, smoke inhalation, carbon monoxide poisoning and electrical shock. Child monitoring devices, such as those described above, have been effective in reducing the number of injuries and deaths related to these common preventable hazards.
However, considering the importance of our children's safety, there remains room for improvement of these systems. One such area for improvement relates to increasing the useful life of a battery used to power the remote unit of these toddler telemetry systems, as they have come to be called.
The remote unit is typically battery operated and, in the event of an emergency, continued and reliable transmission for use in status reporting and direction finding is of paramount importance. In other words, once the hazard is detected and the alarm given, it is essential that the remote unit continue to transmit so that direction finding devices can be used to locate the child.
The remote unit of most child monitoring systems is typically quite small and the available space for a battery is therefore quite limited. Despite recent advances in battery technology, the useful life of a battery is typically related to the battery size. For example, the larger "D" cell lasting considerably longer than the much smaller and lighter "AAA" cell. Though the use of very low power electronic circuits has made possible the use of smaller batteries, a battery's useful life is still very much a factor of its physical size, which, as stated above, is limited because of the small size of a typical remote unit. Therefore, additional efforts to reduce battery drain are important.
Given that much reliance is placed on the reliability of any child monitoring system, it would be desirable for the remote unit to transmit at a low power or not at all when no danger exists. In this way battery life is increased and system reliability is improved overall, since the hazards are usually the exception rather than the rule.